The present invention relates to a II/VI-compound semiconductor light emitting device for use in light emitting devices, such as a light emitting diode and a semiconductor laser and, particularly to a green or blue semiconductor light emitting device.
In a magneto-optical recording for recording or reproducing or recording and reproducing a magneto-optical signal by laser beams, a demand for using a short-wavelength laser, e.g., a blue semiconductor laser as a laser light source is progressively increased in order to improve a recording density. A II-VI ZnMgSSe semiconductor laser receives a remarkable attention as this kind of semiconductor laser.
It is generally difficult to dope a p-type impurity in a II/VI-compound semiconductor, such as ZnSe, ZnSSe and ZnMgSSe. The doping of p-type impurity could be finally realized by using nitrogen N. When N is doped in ZnSe, an upper limit value of a hole concentration is 1.times.10.sup.18 cm.sup.-3. When N is doped in ZnSSe, it is up to 10.sup.17 cm.sup.-3 which is a considerably low value. Since it is confirmed that nitrogen N itself is introduced into a crystal, it is considered that nitrogen N which does not increase hole density is inactivated. Therefore, it is considered that most of such nitrogen N become interlattice atoms.
As shown in FIG. 1 of the accompanying drawings, the ZnMgSSe semiconductor laser made of the II/VI-compound semiconductor has a II/VI-compound semiconductor laser portion 7. The II/VI-compound semiconductor laser portion 7 has an n-GaAs substrate 1, a first cladding layer 2 made of n-ZnMgSSe, a first guide layer 3 made of n-ZNSE with or without S (hereinafter referred to as "ZN(S)Se"), an active layer 4 made of ZnCdSe, a second guide layer 5 made of p-Zn(S)Se, a second cladding layer 6 made of p-ZnMgSSe and an electrode 14 made of In, for example. The first cladding layer 2, the first guide layer 3, the active layer 4, the second guide layer 5 and the second cladding layer 6 are formed on the major surface of the n-GaAs substrate 1, in that order. The electrode 14 is formed on the other surface of the substrate 1 in ohmic contact. The ZnMgSSe semiconductor laser has a p-side electrode portion 12 formed on the II/VI-compound semiconductor laser portion 7. The p-side electrode portion 12 has a first semiconductor layer 8 made of p-Zn(S)Se as a capping layer, a second semiconductor layer 9 having a multiple quantum well (MQW) structure of ZnSE and ZnTe, a third semiconductor layer 10 made of p-ZnTe, an insulating layer 13 made of polyimide, for example, and a p-type metal electrode 11 having a multilayer structure in which Pd, Pt and Au are sequentially deposited. The first semiconductor layer 8, the second semiconductor layer 9, the third semiconductor layer 10 are sequentially formed by epitaxial growth. Then, the second and third semiconductor layers 9, 10 are selectively etched such that their center portions are left in a stripe fashion. The insulating layer 13 is buried in both side portions where the second and third semiconductor layers 9, 10 are removed by etching. The metal electrode 11 is formed on the third semiconductor 10 in ohmic contact.
Although the II/VI-compound semiconductor laser of this kind achieves continuous wave oscillation at room temperature, the II/VI-compound semiconductor laser can continuously oscillate in the order of seconds and is considerably short lifetime. Therefore, the II/VI-compound semiconductor laser could not be applied to an optical pickup device for high-density magneto-optical recording in actual practice.